In recent years, the proliferation is striking of portable terminals provided with communication functions such as mobile telephones, PDA (Personal Digital Assistants), etc., that are portable, and very often imaging devices capable of still image photography or moving image photography such as, for example, digital still cameras or digital movie cameras, etc., are installed in these devices. The restrictions of size (dimensions) and cost on the imaging devices installed in these devices, normally, are very severe. Because of this, compared to the so called independent digital camera, small sized imaging elements with low numbers of pixels are used, and generally an imaging device provided with a single focal point optical system configured using 1 to 3 plastic lenses are adopted. However, advances such as larger numbers of pixels and advanced functions are progressing even in the case of the imaging devices installed in such devices, and because of this, compact variable power optical systems are being demanded that are compatible with imaging elements with large numbers of pixels, and also, that are capable of imaging subjects of photographs distant from the photographer with power ratios exceeding about 2.5 times, and that can be installed in these devices.
As variable power optical systems of imaging devices installed in such devices, there are descriptions, for example, such as in Patent Document 1 to Patent Document 7. A variable power optical system described in Patent Document 1 is an optical system for endoscopes with negative-positive two components with one group fixed. A variable power optical system described in Patent Document 2 is an optical system with negative-positive-negative three components with the feature that the number of constituent lenses is extremely small. A variable power optical system described in Patent Document 3 is an optical system with negative-positive-negative three components in which, relatively, shortening of the overall length has been achieved. A variable power optical system described in Patent Document 4 is an optical system in which, relatively, shortening of the overall length has been achieved, and also, the distortion has been made small. A variable power optical system described in Patent Document 5 is an optical system with negative-positive-negative three components in which the first group is movable. A variable power optical system described in Patent Document 6 is an optical system with negative-positive-negative-positive four components in which the first group is fixed. A variable power optical system described in Patent Document 7 is a variable power optical system with negative-positive-negative-positive four components in which small size is aimed at by making the first group fixed.
Patent Document 1: Japanese Patent Application Publication No. Hei 07(1995)-181377
Patent Document 2: Japanese Patent Application Publication No. 2005-037935
Patent Document 3: Japanese Patent Application Publication No. 2007-058054
Patent Document 4: Japanese Patent Application Publication No. 2007-033555
Patent Document 5: Japanese Patent Application Publication No. 2004-333572
Patent Document 6: Japanese Patent Application Publication No. Hei 09(1997)-179026
Patent Document 7: Japanese Patent Application Publication No. 2006-227129